Answer:
In the New Testament, a bishop is a person who functions as a teaching leader among a local group of Christians. The Greek term episkapos has also been translated as “episcopal,” “elder,” “overseer,” or “pastor.” All refer to the same office and are therefore synonyms.

In the earliest churches, its leaders were simply referred to as “elders.” For example, in Acts 20:17 we read, “Now from Miletus he sent to Ephesus and called the elders of the church to come to him.” In Philippians 1:1, Paul introduces his letter “to all the saints in Christ Jesus who are at Philippi, with the overseers and deacons.” Apparently, there were originally only two leadership positions in the church: elders and deacons.

In the Pastoral Epistles, Paul speaks twice regarding the qualifications of elders, those he considered the leaders of the local church (also notice that these elders generally served as teams rather than as single leaders). In 1 Timothy 3:1-7 we read,

"The saying is trustworthy: If anyone aspires to the office of overseer (bishop), he desires a noble task. Therefore an overseer must be above reproach, the husband of one wife, sober-minded, self-controlled, respectable, hospitable, able to teach, not a drunkard, not violent but gentle, not quarrelsome, not a lover of money. He must manage his own household well, with all dignity keeping his children submissive, for if someone does not know how to manage his own household, how will he care for God's church? He must not be a recent convert, or he may become puffed up with conceit and fall into the condemnation of the devil. Moreover, he must be well thought of by outsiders, so that he may not fall into disgrace, into a snare of the devil."

From this list, we conclude several things. First, the job is a noble task. Second, the job is a limited task (male pronouns and references are used throughout.). Third, integrity is critical (above reproach, committed to his spouse, clear thinking, self-controlled, well respected, friendly, not influenced by alcoholic drinks, not violent or argumentative, not greedy, caring for his children, and having a good reputation among the unchurched). Fourth, he must have the ability to teach. (Deacons, whose requirements are listed in the next verses, are not required to have teaching ability.) Titus 1:5-7 shares a similar list for elders, but it adds the ability to rebuke false teaching. When Peter wrote to this group of church leaders, he called himself a “fellow elder” (1 Peter 5:1).

The earliest writings of the church fathers also seem to confirm this role of bishops as the teaching leaders who served alongside deacons to oversee the church. Both Clement of Rome (c. 95) and the Didache referred to elders and deacons from the late early first century to the early second century as the church’s leaders.

Over time, additional layers of leadership were added to the church. Eventually, the term bishop came to be applied to a regional church leader who administered many churches. At the Council of Nicea in A.D. 325, the church leader of each city or area represented his region’s churches. These leaders were referred to as “bishops.” Many Christian traditions continue to embrace this role of bishops today.

However, the biblical teaching is that elders and deacons lead local churches. The elder was also known as a bishop or pastor and functioned in that role. This does not make additional church leadership roles wrong (to meet important needs for regional or national leadership among groups of churches), but indicates that Scripture points to elders and deacons as the local church leaders.